What physiological reaction happens to superficial vessels during heat syncope?

During heat syncope, the physiological reaction that occurs involves the pooling of blood in the superficial vessels, which leads to a decrease in blood pressure. When the body is subjected to high external temperatures, blood vessels dilate to help dissipate heat, which can result in blood accumulating in the peripheral areas rather than being returned effectively to the heart. This pooling reduces the volume of blood available to maintain adequate blood pressure and cerebral perfusion, making the individual susceptible to fainting or syncope.

The other physiological responses suggested in the options do not accurately describe what transpires during heat syncope. For instance, blood vessel constriction would not occur because the body is trying to cool itself through vasodilation. Likewise, while blood flow may increase in other areas of the body in specific conditions, the scenario of increased blood flow to the head is not typical during heat syncope. Elevation of body temperature is a result of the conditions leading to heat syncope, but it is not the physiological change within the vessels responsible for the event itself. The critical takeaway is that the impaired circulation due to blood pooling is the key factor that leads to the syncope experienced in heat-related conditions.